This invention pertains to emulsion polymerization of ethylenically unsaturated monomers in an aqueous medium and particularly to epoxy modified emulsion polymers.
Epoxy modified polymers are shown in U.S. Pat. No. 4,028,294 wherein epoxy resins described as polyepoxides of dihydric phenols such as bisphenols are blended with acrylic monomers and emulsion polymerized to provide thermosetting latex particles. Similarly, U.S. Pat. No. 3,970,628 discloses emulsion polymerized monomers containing epoxy resins.
It now has been found that substantially improved epoxy modified emulsion polymers can be produced by providing an epoxy blend of epoxy resin with glycidyl acrylate, glycidyl methacrylate or other oxirane containing ethylenic monomer. This epoxy blend can be produced by including the epoxy resin in the emulsion reaction medium by dissolving the epoxy resin in ethylenically unsaturated monomers prior to being added to the aqueous medium or by adding the epoxy resin simultaneously with the ethylenically unsaturated monomer as a separate pre-emulsified portion. The epoxy modified emulsion polymers of this invention provide substantially improved latices suitable for use as ambient or low temperature thermosetting film-forming binder for protective coatings. The cured coating exhibit improved salt spray resistance, solvent resistance, impact resistance as well as other desirable cured film integrity properties. These and other advantages will become more apparent by referring to the detailed Description of the Invention.